1. Field of the Invention
The present invention relates to a fluid gear pump of the gerotor type, which is suited for use as a lubricant pump within machinery such as an automotive engine.
2. Disclosure Information
Gerotor lubricating oil pumps have been used for years within automotive engines. U.S. Pat. No. 5,738,501 discloses a gear pump in which internal valving is used to adjust the amount of fluid being discharged from the pump. A drawback of the pump disclosed in the '501 patent resides in the fact that the efficiency of the pump is impaired by the use of the illustrated internal passage output limiting system.
For any particular automotive engine, designers will typically specify a lubrication pump having a volume rate of flow which is sufficient to provide adequate lubrication under worst case conditions. Conditions which dictate maximum lubricant flow generally correspond to maximum temperature, high speed operation, whereas conditions which dictate maximum flow per pump revolution (conditions that dictate the pump's displacement) generally correspond to maximum temperature, low speed operation. Conventionally, a pressure regulating valve installed between the oil pump's outlet and inlet is the only control mechanism for the pump. In the event that the pressure differential between the outlet and inlet exceeds a set value, the pressure regulating valve limits the pressure differential by allowing some of the pump's outlet flow to return directly to the pump inlet, effectively bypassing the engine's lubrication circuit. This method of control wastes energy for two reasons: first, because oil which has been pumped to a high pressure is merely bled to some lower pressure location, the work needed to pressurize the oil is lost. Secondly, the engine's bearings do not always require oil pressure as high as the pressure regulating valve setting, and excessive oil flow through the bearings causes increased energy consumption by depressing the temperature of oil actually in contact with the bearing journals, thereby increasing the oil's viscosity and the shear work performed on the oil. In any case, fuel consumption needlessly increases. The present gerotor pump allows operation so as to control the volumetric output of the pump, thereby permitting the pump output to be matched to the engine's requirements.